Conventional adhesion primers for adhesives and paints are usually low solids content polymer solutions in an organic solvent such as methylethylketone or various other hydrocarbon and chlorinated hydrocarbon solvents. In the process of depositing the primers on adherends, large amounts of solvents must be evaporated and released into the atmosphere. The released solvents are a contributing factor to the pollution problems that are prevalent in many areas of the country.
In U.S. Pat. No. 3,823,103, aqueous dispersions are disclosed that contain a heat-hardenable phenolic resin. The dispersions are prepared by refluxing a mixture of a phenol and an aldehyde in an aqueous reaction medium containing an alkaline catalyst to produce a phenolic resin and then adding a mixture of gums to the mixture. The dispersions are indicated to be useful in applications wherein mineral fibers are sprayed with the dispersions and subsequently formed into mineral fiber batts. The dispersions described in the patent would be unsuitable for use as primers for several reasons, including the presence of a corrosive alkaline material and the insolubility of the phenolic resin in the aqueous medium.
It is a principal object of this invention to provide water soluble oligomeric primers which can be used to replace organic solvent based primers.
Another object of the invention is to provide water soluble phenol-formaldehyde and resorcinol-formaldehyde oligomers that are effective as adhesion primers for the adhesive bonding of aluminum alloys and as protective coatings for aluminum.
A further object of the invention is to provide a process for preparing the primer formulations.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.